I would hope that it's both, that when you Steemit Upvote, you're playing a betting game, like gambling, which means rewards, money, depending on how good you play the voting game; and it is also curation if you resteem it or it is curated (moved) to the trending page. Also, more people may consider reading it if it made more money. For example, if I saw a post that made like $50,000, then I would click on it because I don't think any post has ever made that much money on Steemit. So, money talks. If I had to pick one or the other, I would say it is not really curation and it is mostly a gambling game which involves possibly winning some money for betting and that also means, as seen with all those people who buy lottery tickets, that many people lose and make either no money or very little and that is kind of how it works. If everybody won, then it might not be a game.